Continuously Operating He3 Refrigerator for Producing Temperatures down to ¼°K

A continuously acting, portable, He3 refrigerator is described. The He3 is recirculated in a system that operates without mechanical pumps. The throttling of the returning liquid is accomplished by means of a porous plug. Good regulation is obtained by using a system that allows the pressure across the porous plug to vary with the circulation rate. The lowest temperature reached while circulating is 0.26°K at zero ``external'' heat input, and 0.40°K at 2mw.